The present invention is based on a fuel metering device and method for an internal combustion engine with a lambda regulator and a warm-up enrichment, in which at the onset of regulation the warm-up enrichment is reduced or turned off. Such a fuel metering system is already known under the trademark "L-Jetronic". In this system the metering device changes from regulating mode to lambda regulating mode at a time when at least the exhaust sensor has reached its working temperature and therefore is ready. As a rule, warm-up enrichment processes are temperature-dependent in their starting values and are regulated as a function of time.
It has been shown that this known system is not always able to provide a clean exhaust gas under certain operational circumstances because of mixture compositions which are not ideal in these special operational circumstances. This is based on the following physical factors. If the lambda sensor has not been sufficiently heated, it cannot work correctly, except with long idle times. For this reason the result is a mixture not equal to lambda=1 (rich or lean) for relatively long periods of time, which deficiency leads to strong exhaust emissions. This problem becomes especially noticeable during the change from overrun to normal driving conditions.
During overrun the lambda regulator aims for a median lambda value onto which is superimposed the normally multiplicatively-acting warm-up enrichment during the warm-up phase. The lambda regulator goes again into action at the end of the overrun and, because of the relatively slow lambda sensor, it takes a comparatively long time until the lambda regulator with its several switching points goes into action.